This application claims the priority of German Patent Application 199 12 890.1, filed Mar. 23, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for controlling an internal combustion engine with a mechanically driven supercharger which can be switched on and off by means of a clutch and is arranged in a charge-air line, a bypass-air line with a bypass-air control element connecting the intake and delivery sides of the supercharger, a throttle valve being situated upstream of the supercharger or downstream in the charge-air line, and an engine control unit controlling the clutch and/or the bypass-air control element with specifiable values for a degree of opening and/or a switching state of the clutch.
In the case of internal combustion engines, superchargers driven mechanically by the latter are generally used to boost the full-load torque of the internal combustion engine. To improve fuel consumption in the part-load range of the internal combustion engine, the supercharger is switched on and off as required by means of a clutch. It is thus possible to save the driving power for the supercharger when the supercharger is switched off. When the supercharger is switched on by means of the clutch, the driver feels a distinct switch-on jerk, particularly in the upper part-load range, this being caused by a sag in the torque of the internal combustion engine due to the mass moment of inertia of the supercharger during its acceleration. This phenomenon occurs especially when accelerating from part load, and the jerk is all the greater, the greater the load when switching on. The smallest jerk is obtained if the supercharger is switched on directly above the idling range during an acceleration process. Since this operating range of the internal combustion engine up to the switching on of the supercharger is very small, the advantage in terms of consumption dwindles.
German Patent Document DE 195 33 333 C2 discloses a method for controlling a supercharged internal combustion engine in which a supercharger is arranged in a charge-air line and can be switched on and off by means of a clutch. A throttle valve is arranged upstream or downstream of the supercharger. A bypass-air line connects the intake and delivery sides of the supercharger. A bypass-air control element controls and regulates flow through the bypass-air line. It is controlled together with the clutch of the supercharger by an engine control system as a function of operating states and operating parameters of the internal combustion engine. To avoid jerking when switching on and off, the clutch is permanently closed during cruise-control operation above a speed threshold, which is preferably subject to hysteresis. For the transition from overrun cut-off to engine-driven operation, provision is furthermore made for the clutch to be activated in a defined manner only after the resumption of combustion. As an alternative, the clutch can be controlled by means of a regulated-current output stage, or the torque of the internal combustion engine can be raised by influencing the throttle-valve angle in a defined manner, thus compensating for the sag in torque.
German Patent Document DE 35 12 408 A1 has disclosed an internal combustion engine with a supercharger which is driven mechanically by the internal combustion engine via a clutch. When a specified load signal occurs, the flow of fresh gas is initially switched from a bypass line which bypasses the supercharger to the supercharger before the clutch is closed, with the result that rotation is imparted to the supercharger by the fresh air drawn in. This is intended to avoid operating shocks when closing the clutch. Since, before the clutch is closed, the supercharger must first be brought up to a sufficient rotational speed to avoid the operating jerk, the process of switching on the supercharger is delayed.
An object on which the invention is based is, by simple means, to reduce the jerk when the supercharger is switched on in the part-load range. According to the invention, it is achieved by a system of the above noted type, wherein in a specified part-load range of the internal combustion engine, the bypass-air control element closes the bypass-air line as soon as the clutch is open.
According to the invention, the switching off of the supercharger can be extended to the maximum possible range. Favourable part-load consumption figures are thereby obtained. To avoid the severe switch-on jerk in these operating ranges, the bypass-air control element closes the bypass-air line when the clutch is open. The internal combustion engine thus draws the charge air in via the supercharger and the flowing air imparts a rotary motion to the rotors of the supercharger. Measurements have shown that, in the case of a Roots blower as a supercharger, the rotational speed of the supercharger reaches approximately the speed of the internal combustion engine. Since the supercharger rotates continuously in intake mode, the jerk caused by the mass moment of inertia when engaging the clutch of the supercharger is reduced. The rotational speed of the supercharger can be influenced in an advantageous manner when the clutch is open if the bypass-air control element closes the bypass-air line to a greater or lesser extent.
In combination with the measures proposed, it may be expedient according to certain contemplated embodiments of the invention to increase the torque of the internal combustion engine while the clutch is being engaged. This can be accomplished by opening the fuel metering element, e.g. in the form of a throttle valve, of the internal combustion engine. The ignition and/or the camshaft of the internal combustion engine can furthermore be adjusted accordingly and/or use can be made of the switchability of the intake pipe.
Further advantages will become apparent from the following description of the drawing. The drawing shows an illustrative embodiment of the invention. The description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them to give further worthwhile combinations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.